Astronomers discover a huge, dark secret in galaxy NGC 4889

While it may look calm in photographs, researchers using the Hubble Space Telescope to study giant elliptical galaxy NGC 4889 have learned that it is quietly home to what may be the largest supermassive black hole in the universe, or at the very least one of the biggest.

Located approximately 300 million light years away in the Coma Cluster, NGC 4889 contains a black hole that is 21 billion times more massive than the Sun and which has an event horizon that is nearly 130 billion kilometers in diameter, or 15 times bigger than the orbit of Neptune.

That’s considerably larger than the supermassive black hole at the center of the Milky Way, the ESA/Hubble Information Center said in a statement. Our galaxy’s black hole has a mass of only four million times the Sun’s and an event horizon one-fifth as large as Mercury’s orbit.

NGC 4889’s black hole is no longer active, the Center noted. It is no longer consuming stars or dust and is currently taking the cosmic equivalent of a post-Thanksgiving nap. Meanwhile, the galaxy’s serene environment has allowed new stars to form from the previously consumed dust and gas. The galaxy’s contents are currently orbiting the black hole undisturbed.

Catching a nap before its next meal arrives

That wasn’t always the case, the researchers explained. When it was active, this supermassive black hole collected material through its gravitational pull in a process known as accretion. Gas, dust and other galactic debris slowing fell inwards to the black hole during this time, and as it accumulated, it formed a spinning disc of matter referred to as an accretion disc.

The accretion disc orbited the black hole and was accelerated by the immense gravitational pull of the tremendous entity, causing to be heated to temperatures of several million degrees. As the material heated, it also began to expel very large and high energetic jets. The galaxy would have been classified as a quasar during this period of activity, the Center said, and the disc around the supermassive black hole would have emitted 1,000 times more energy than the Milky Way.

Once there was no more nearby galactic material for the black hole to gorge itself on, it entered a dormant period while waiting for more matter to consume. In the meantime, astronomers can use it to learn more about how and where quasars originally formed during the early universe.

While the researchers note that it is impossible to directly observe black holes, as light is unable to escape their gravitational pulls, its mass can be determined indirectly by measuring the speed of the stars travelling around the galaxy’s center. Since the velocity of those stars are dependent upon the mass of the object around which they orbit, they could be used to determine the mass of the supermassive black hole at the center of NGC 4889.

—–

Feature Image: This image shows the elliptical galaxy NGC 4889 in front of hundreds of background galaxies, and deeply embedded within the Coma galaxy cluster. Well-hidden from human eyes, there is a gigantic supermassive black hole at the centre of the galaxy. (Credit: NASA & ESA)